1. Field Of The Invention
The present invention relates generally to well treating fluids and additives therefor, and more particularly, to additives for reducing the water loss and improving other properties of drilling fluids, stimulation fluids, cement slurries and the like.
2. Description Of The Prior Art
A great variety of aqueous treating fluids are utilized in the drilling, completion, stimulation and workover of oil and gas wells. Examples of such fluids are aqueous drilling fluids which generally contain clays and clayey materials such as bentonite; aqueous completion and stimulation fluids which contain hydratable gelling agents such as galactomannan gums, cellulose derivatives and various polymers; and aqueous completion fluids containing cement, i.e., cement slurries. In the use of all of such fluids, particularly in the hostile high temperature subterranean environments to which the fluids are subjected in deep wells, problems are encountered which involve the loss of water from the fluids to surrounding formations and/or undesirable increases or decreases in viscosity and other rheological properties of the fluids.
In the drilling of well bores, the aqueous drilling fluids are normally comprised of water, various types of finely divided clays and weighting materials, all suspended in the water. The drilling fluid functions to remove cuttings from the well bore as it is being drilled; to prevent excessive amounts of water from flowing from the well bore into surrounding formations by depositing substantially water impervious filter cake on the walls of the well bore; to hold the cuttings and solids in suspension; and to exert sufficient pressure in the well bore to prevent pressurized fluids contained in penetrated subterranean formations from intruding into the well bore.
When certain subterranean formations such as gypsum are encountered, the viscosity of the drilling fluid can become too high due to flocculation of the clay particles therein. In deeper wells, the high temperature environment encountered by the drilling fluid can cause excessive water loss and increased viscosity to occur. When the viscosity of the drilling fluid reaches too high a level for whatever cause, pump pressures required for circulating the drilling fluid greatly increase and circulation may be slowed or stopped. The same or similar types of problems can be encountered in the use of aqueous stimulation fluids, aqueous cement slurries, and other well treating fluids when high temperature subterranean formations are encountered.
In order to control water loss and prevent changes in viscosity and other rheological properties of aqueous well treating fluids, a variety of additives have heretofore been included therein. Additives for reducing water loss have included various natural and synthetic polymers which act as colloidal agents. The yield point, gel strength, and in turn, the apparent viscosity of well treating fluids, have heretofore commonly been controlled by including organic additives which function as dispersants in the well treating fluid such as complex phosphates, alkalies, lignites, tannins, lignosulfonates, asphalts, etc.
Lignites and lignite derivatives are particularly effective in controlling viscosity and other rheological properties of well treating fluids subjected to high temperatures. Plant tannins such as quebracho and sulfomethylated quebracho are effective dispersants in contaminated drilling fluids and other well treating fluids at high temperatures. Other dispersants which have been utilized heretofore include sulfonated asphalts, lignosulfonates and similar organic materials.
While, as mentioned, many additives for reducing water loss and improving the rheological properties of well treating fluids have been developed and used heretofore, such additives have generally been expensive and/or have high toxicity whereby their use involves disposal problems in many areas. Thus, there is a continuous demand for more effective and economical additives having low toxicity.